One-step synthesis of carbon nitride catalyzed by trace ferric salt for methylene blue photodegradation: the effect of anionic media

Herein, a facile one-step method was developed to achieve the Fe₂O₃-doped graphitic carbon nitride (CN) using KCl/NaCl eutectic salts as the high temperature solvent and urea as the starting material in the presence of trace ferric salt. The results indicated that trace ferric salt catalyzed the formation of CN with a noticeably enhanced yield. The anionic media⁻paired to Fe³⁺, i.e. NO₃⁻, SO₄²⁻ or Cl⁻, has an important influence on the element wt. %, C/N mole ratio, band gap energy and photocatalytic performance of CN. CN-FN, prepared by the catalysis of Fe(NO₃)₃·9H₂O, owns a triazinimide (TI) structural unit (C₃N₃) with a band gap energy of 2.03 eV, high oxygen content of 5.33 wt.%. CN-FS and CN-FC, fabricated by the catalysis of Fe₂(SO₄)₃ and FeCl₃·6H₂O, respectively, tend to form a higher nitrogen content of carbon-nitrogen materials such as C₆N₇ and C₄N₆ and a lower oxygen content of 0.42 and 0.81 wt.%. The adsorption-photodegradation performance of CN-FN for methylene blue (MB) is obviously superior to that of CN-FS or CN-FC due to the remarkably structural differences among them. The reactive species studies indicate that the photo-generated holes and ¹O₂ are primary active species for MB degradation. The present work may provide a new insight for design of efficient polymeric materials toward practical applications in environment and energy chemistry.